Electrolytic capacitor for use in an implantable medical device

ABSTRACT

A capacitor structure comprises a shallow drawn case having a first major side and a peripheral wall extending therefrom, the first major side having a first interior surface and the wall having a peripheral interior surface. A lid is sealingly coupled to the case along adjacent edges of the lid and the wall, the lid and said case forming an encasement of the capacitor structure, the lid comprising a second interior surface. A cathode material is disposed proximate the first and second interior surfaces, and an anode is positioned intermediate the cathode material and has a peripheral portion positioned proximate the adjacent edges. A protective layer on the peripheral portion protects the anode during the sealing process. A first insulative separator is positioned between the anode and the cathode material.

FIELD OF THE INVENTION

The present invention generally relates to capacitors, and moreparticularly to a thin electrolytic capacitor suitable for use in animplantable medical device such as an implantable cardiac defibrillator(ICD).

BACKGROUND OF THE INVENTION

ICDs are devices that are typically implanted in a patient's chest totreat very fast, and potentially lethal, cardiac arthythmias. Thesedevices continuously monitor the heart's electrical signals and senseif, for example, the heart is beating dangerously fast. If thiscondition is detected, the ICD can deliver one or more electric shocks,within about five to ten seconds, to return the heart to a normal heartrhythm. These defibrillation electric shocks may range from a fewmicro-joules to very powerful shocks of approximately twenty-five joulesto forty joules.

Early generations of ICDs utilized high-voltage, cylindrical capacitorsto generate and deliver defibrillation shocks. For example, standard wetslug tantalum capacitors generally have a cylindrically shapedconductive casing serving as the terminal for the cathode and a tantalumanode connected to a terminal lead electrically insulated from thecasing. The opposite end of the casing is also typically provided withan insulator structure.

One such capacitor is shown and described in U.S. Pat. No. 5,369,547issued on Nov. 29, 1994 and entitled “Capacitor”. This patent disclosedan electrolytic capacitor that includes a metal container that functionsas a cathode. A porous coating, including an oxide of a metal selectedfrom the group consisting of ruthenium, iridium, nickel, rhodium,platinum, palladium, and osmium, is disposed proximate an inside surfaceof the container and is in electrical communication therewith. A centralanode selected from the group consisting of tantalum, aluminum, niobium,zirconium, and titanium is spaced from the porous coating, and anelectrolyte within the container contacts the porous coating and theanode.

U.S. Pat. No. 5,737,181 issued on Apr. 7, 1998 and entitled “Capacitor”describes a capacitor that includes a cathode material of the typedescribed in the above cited patent disposed on each of two opposedconducting plates. A metal anode (also of the type described in theabove cited patent) is disposed between the cathode material coating andthe conducting plates.

U.S. Pat. No. 5,982,609 issued Nov. 9, 1999 and entitled “Capacitor”describes a capacitor that includes a cathode having a porous coatingincluding an amorphous metal oxide of at least one metal selected fromthe group consisting of ruthenium, iridium, nickel, rhodium, rhenium,cobalt, tungsten, manganese, tantalum, molybdenum, lead, titanium,platinum, palladium, and osmium. An anode includes a metal selected fromthe group consisting of tantalum, aluminum, niobium, zirconium, andtitanium.

While the performance of these capacitors was acceptable fordefibrillator applications, efforts to optimize the mechanicalcharacteristics of the device have been limited by the constraintsimposed by the cylindrical design. In an effort to overcome this, flatelectrolytic capacitors were developed. U.S. Pat. No., 5,926, 362 issuedon Jul. 20, 1999 and entitled “Hermetically Sealed Capacitor” describesa deep-drawn sealed capacitor having a generally flat, planar geometry.The capacitor includes at least one electrode provided by a metallicsubstrate in contact with a capacitive material. The coated substratemay be deposited on a casing side-wall or connected to a side-wall. Thecapacitor has a flat planar shape and utilizes a deep-drawn casingcomprised of spaced apart side-walls joined at their periphery by asurrounding intermediate wall. Cathode material is typically depositedon an interior side-wall of the conductive encasement which serves asone of the capacitor terminals; e.g. the cathode. The other capacitorterminal (the anode) is isolated from the encasement by aninsulator/feedthrough structure comprised of, for example, aglass-to-metal seal. It is also known to deposit cathode material on aseparate substrate that is placed in electrical communication with thecase. In another embodiment, the cathode substrate is insulated from thecase using insulators and a separate cathode feedthrough.

A valve metal anode made from metal powder is pressed and sintered toform a porous structure, and a wire (e.g. tantalum) is imbedded into theanode during pressing to provide a terminal for joining to thefeedthrough. A separator (e.g. polyolefin, a fluoropolymer, a laminatedfilm, non-woven glass, glass fiber, porous ceramic, etc.) is providedbetween the anode and the cathode to prevent short circuits between theelectrodes. Separator sheets are sealed either to a polymer ring thatextends around the perimeter of the anode or to themselves.

A separate weld ring and polymer insulator may be utilized for thermalbeam protection as well as anode immobilization. Prior to encasementwelding, a separator encased anode is joined to the feedthrough wire by,for example, laser welding. This joint is internal to the capacitor. Theouter metal encasement structure is comprised essentially of twosymmetrical half shells that overlap and are welded at their perimeterseam to form a hermetic seal. After welding, the capacitor is filledwith electrolyte through a port in the encasement.

The above described techniques, present concerns relating to both devicesize and manufacturing complexity. The use of overlapping half-shieldsresults in a doubling of the encasement thickness around the perimeterof the capacitor thus reducing the available interior space for thecapacitor's anode. This results in larger capacitors. Space for theanode material is further reduced by the presence of the weld ring andspace insulator. In addition, manufacturing processes become morecomplex and therefore more costly, especially in the case of adeep-drawn encasement.

A further disadvantage of the known design involves the complexity ofthe anode terminal-to-feedthrough terminal weld joint. As was described,a tantalum anode lead is imbedded into the anode and is joined via laserwelding to a terminal lead of the feedthrough. This is typicallyaccomplished by forming a “J” or “U” shape with one or more of theleads, pressing the terminal end of these leads together, and laserwelding the interface. In order to accomplish this, one must eitherperform this step prior to welding the feedthrough ferrule into theencasement or sufficient space must be provided in the capacitor anodestructure to facilitate clamping and welding while the anode is in thecase. This results in additional manufacturing complexity while thelatter negatively impacts device size.

As stated previously, a separator material is provided on the anode andmay be sealed to itself to form an envelope. The anode is typically onthe order of 0.1 inch thick. As a result, the sealing operation iscomplex, and significant separator material typically overhangs theanode. This overhang must be accommodated in the design and typicallyeither reduces the size of the anode or increases the size of thecapacitor. Furthermore, due to the proximity of thermally sensitiveseparator material to the encasement, the separator is in direct contactwith the cathode/encasement structure. Weld parameters must therefore becarefully selected to prevent thermal damage of the separator material.When cathode material is deposited on a separate substrate, as describedabove, substrate thickness further reduces the space available for anodematerial or increases the size of the capacitor.

Thus, while the development of flat electrolytic capacitorssignificantly reduces size and thickness, defibrillation capacitors arestill the largest components in current ICDs making further downsizing aprimary objective.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a capacitorstructure, comprising a shallow drawn case having a first major side anda peripheral wall extending therefrom, the first major side having afirst interior surface and the wall having a peripheral interiorsurface. A lid is sealingly coupled to the case along adjacent edges ofthe lid and the wall, the lid and the case forming an encasement of thecapacitor structure, the lid comprising a second interior surface. Acathode material is disposed proximate the first and second interiorsurfaces, and an anode is positioned intermediate the cathode materialand has a peripheral portion positioned proximate the adjacent edges. Aprotective layer on the peripheral portion protects the anode during theencasement sealing process. A first insulative separator is positionedbetween the anode and the cathode material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a cross-sectional view of an electrolytic capacitor inaccordance with the teachings of the prior art;

FIGS. 2, 3, and 4 are front, side, and top cross-sectional views of aflat electrolytic capacitor in accordance with the teachings of theprior art;

FIGS. 5, 6, and 7 are front cross-sectional, side cross-sectional, andscaled cross-sectional views of an electrolytic capacitor in accordancewith a first embodiment of the present invention and suitable for use inan implantable medical device;

FIGS. 8, and 9 are side cross-sectional and scaled cross-sectional viewsof an electrolytic capacitor in accordance with a further embodiment ofthe present invention;

FIG. 10 is a cross-sectional view of a capacitor/anode encasementstructure in accordance with the teachings of the prior art;

FIG. 11 is a cross-sectional view of a novel capacitor/anode encasementassembly;

FIG. 12 is a cross-sectional view of an alternative capacitor/anodeencasement assembly;

FIG. 13 illustrates a first novel technique for electrically coupling ananode lead wire through a ferrule in an electrolytic capacitor; and

FIGS. 14-18 illustrate alternate techniques for electrically coupling ananode lead wire through a ferrule in an electrolytic capacitor.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the scope, applicability, orconfiguration of the invention in any way. Rather, the followingdescription provides a convenient illustration for implementingexemplary embodiments of the invention. Various changes to the describedembodiments may be made in the function and arrangement of the elementsdescribed herein without departing from the scope of the invention.

FIG. 1 is a cross-sectional view of an electrolytic capacitor inaccordance with the teachings of the prior art. It comprises acylindrical metal container 20 made of, for example tantalum. Typically,container 20 comprises the cathode of the electrolytic capacitor andincludes a lead 22 that is welded to the container. An end scat of cap24 includes a second lead 26 that is electrically insulated from theremainder of cap 24 by means of a feed-through assembly 28. Cap 24 isbonded to container 20 by, for example, welding. Feed-through 28 of lead26 may include a glass-to-metal seal through which lead 26 passes. Ananode 30 (e.g., porous sintered tantalum) is electrically connected tolead 26 and is disposed within container 20. Direct contact betweencontainer 20 and anode 30 is prevented by means of electricallyinsulating spacers 32 and 34 within container 20 that receive oppositeends of anode 30. A porous coating 36 is formed directly on the innersurface of container 20. Porous coating 36 may include an oxide ofruthenium, iridium, nickel, rhodium, platinum, palladium, or osmium. Asstated previously, anode 30 may be made of a sintered porous tantalum.However, anode 30 may be aluminum, niobium, zirconium, or titanium.Finally, an electrolyte 38 is disposed between and in contact with bothanode 30 and cathode coating 36 thus providing a current path betweenanode 30 and coating 36. As stated previously, while capacitors such asthe one shown in FIG. 1 were generally acceptable for defibrillatorapplications, optimization of the device is limited by the constraintsimposed by the cylindrical design.

FIGS. 2, 3, and 4 are front, side, and top cross-sectional viewsrespectively of a flat electrolytic capacitor, also in accordance withthe teachings of the prior art, designed to overcome some of thedisadvantages associated with the electrolytic capacitor shown in FIG.1. The capacitor of FIGS. 2, 3, and 4 comprises an anode 40 and acathode 44 housed inside a hermetically sealed casing 46. The capacitorelectrodes are activated and operatively associated with each other bymeans of an electrolyte contained inside casing 46. Casing 46 includes adeep drawn can 48 having a generally rectangular shape and comprised ofspaced apart side-walls 50 and 52 extending to and meeting with opposedend walls 54 and 56 extending from a bottom wall 58. A lid 60 is securedto side-walls 50 and 52 and to end walls 54 and 56 by a weld 62 tocomplete an enclosed casing 46. Casing 46 is made of a conductive metaland serves as one terminal or contact for making electrical connectionsbetween the capacitor and its load.

The other electrical terminal or contact is provided by a conductor orlead 64 extending from within the capacitor through casing 46 and, inparticular, through lid 60. Lead 64 is insulated electrically from lid60 by an insulator and seal structure 66. An electrolyte fill opening 68is provided to permit the introduction of an electrolyte into thecapacitor, after which opening 68 is closed. Cathode electrode 44 isspaced from the anode electrode 40 and comprises an electrode activematerial 70 provided on a conductive substrate. Conductive substrate 70may be selected from the group consisting of tantalum, nickel,molybdenum, niobium, cobalt, stainless steel, tungsten, platinum,palladium, gold, silver, cooper, chromium, vanadium, aluminum,zirconium, hafnium, zinc, iron, and mixtures and alloys thereof. Anode40 may be selected from the group consisting of tantalum, aluminum,titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium,silicon, germanium, and mixtures thereof. A separator structure includesspaced apart sheets 72 and 74 of insulative material (e.g. a microporouspolyolefinic film). Sheets 72 and 74 are connected to a polymeric ring76 and are disposed intermediate anode 40 and coated side-walls 50 and52 which serve as a cathode electrode.

As already mentioned, the above described capacitors present certainconcerns with respect to device size and manufacturing complexity. Incontrast, FIGS. 5, 6, and 7 are front cross-sectional, sidecross-sectional, and scaled cross-sectional views of an electrolyticcapacitor suitable for use in an implantable medical device inaccordance with a first embodiment of the present invention. As can beseen, one or more layers of an insulative polymer separator material 142(e.g. micro-porous IFRE or polypropylene) are heat sealed around a thin,D-shaped anode 140 (e.g. tantalum) having an anode lead wire 144 (e.g.tantalum) embedded therein. Capacitor grade tantalum powder such as the“NH” family of powders may be employed for this purpose. These tantalumpowders have a charge per gram rating of between approximately 17,000 to23,000 microfarad-volts/gram and have been found to be well suited forimplantable cardiac device capacitor applications. Tantalum powders ofthis type are commercially available from HC Starck, Inc. located inNewton, Mass.

Before pressing, the tantalum powder is typically, but not necessarily,mixed with approximately 0 to 5 percent of a binder such as ammoniumcarbonate. This and other binders are used to facilitate metal particleadhesion and die lubrication during anode pressing. The powder andbinder mixture are dispended into a die cavity and are pressed to adensity of approximately 4 grams per cubic centimeter to approximately 8grams per cubic centimeter. After pressing, it is sometimes beneficialto modify anode porosity to improve conductivity within the internalportions of the anode. Porosity modification has been shown tosignificantly reduce resistance. Macroscopic channels are incorporatedinto the body of the anodes to accomplish this. Binder is then removedfrom the anodes either by washing in warm deionized water or by heatingat a temperature sufficient to decompose the binder. Complete binderremoval is desirable since residuals may result in high leakage current.Washed anodes are then vacuum sintered at between approximately 1,350degrees centigrade and approximately 1,600 degrees centigrade topermanently bond the metal anode particles.

An oxide is formed on the surface of the sintered anode by immersing theanode in an electrolyte and applying a current. The electrolyte includesconstituents such as water and phosphoric acid and perhaps other organicsolvents. The application of current drives the formation of an oxidefilm that is proportional in thickness to the targeted forming voltage.A pulsed formation process may be used wherein current is cyclicallyapplied and removed to allow diffusion of heated electrolyte from theinternal pores of the anode plugs. (See U.S. patent application Ser. No.10/261,066 filed Sep. 30, 2002 entitled “Method and Apparatus forMaintaining Energy Storage in an Electrical Storage Device” theteachings of which are hereby incorporated by reference.) Intermediatewashing and annealing steps may be performed to facilitate the formationof a stable, defect free, oxide.

Layers of cathode material 146 are deposited on the inside walls of athin, shallow drawn, D-shaped casing 148 (e.g. titanium) having firstand second major sides and a peripheral wall, each of which have aninterior surface. The capacitive materials may be selected from thosedescribed above or selected from the group including graphitic or glassycarbon on titanium carbide, carbon and silver vanadium oxide on titaniumcarbide, carbon and crystalline manganese dioxide on titanium carbide,platinum on titanium, ruthenium on titanium, barium titanate ontitanium, carbon and crystalline ruthenium oxide on titanium carbide,carbon and crystalline iridium oxide on titanium carbide, silvervanadium oxide on titanium, and the like.

Anode 140 and cathode material 146 are insulated from each other bymeans of a micro-porous polymer separator material such as a PTFEseparator of the type produced by W. L. Gore, Inc. located in Elkton,Md. or polypropylene of the type produced by Celgard, Inc. located inCharlotte, N.C. Separators 146 prevent physical contact and shorting andalso provide for ionionic conduction. The material may be loosely placedbetween the electrodes or can be sealed around the anode and/or cathode.Common sealing methods include heat sealing, ultra sonic bonding,pressure bonding, etc.

The electrodes are housed in a shallow drawn, typically D-shaped case(e.g. titanium) that may have a material thickness approximately 0.005to 0.016 inches thick. A feed-through 150 is comprised of a ferrule 154(e.g. titanium), a terminal lead wire 152 (e.g. tantalum), and aninsulator 156 (e.g. a polycrystalline ceramic polymer, non-conductingoxides, conventional glass, etc.) is bonded to ferrule 154 and lead wire152. Sealed anode 140 is inserted into a cathode coated case and aspacer ring is inserted around the periphery of the anode to secure theposition of the anode within the case. A J-shaped feed-though lead wire152 is electrically coupled to anode lead wire 144 as, for example, byresistance or laser welding. In accordance with an aspect of the presentinvention, lead wire 152 may be joined to anode lead wire 144 withoutthe necessity for a J-shaped bend as will be fully described hereinbelowand as represented in FIG. 8. The lid is positioned and secured in thecase by welding.

After assembly and welding, an electrolyte is introduced into the casingthrough a fill-port 160. The electrolyte is a conductive liquid having ahigh breakdown voltage that is typically comprised of water, organicsolvents, and weak acids or of water, organic solvents and sulfuricacid. Filling is accomplished by placing the capacitor in a vacuumchamber such that fill-port 160 extends into a reservoir of electrolyte.When the chamber is evacuated, pressure is reduced inside the capacitor.When the vacuum is released, pressure inside the capacitorre-equilibrates, and electrolyte is drawn through fill-port 160 into thecapacitor.

Filled capacitors are aged to form an oxide on the anode leads and otherareas of the anode. Aging, as with formation, is accomplished byapplying a current to the capacitor. This current drives the formationof an oxide film that is proportional in thickness to the targeted agingvoltage. Capacitors are typically aged approximately at or above theirworking voltage, and are held at this voltage until leakage currentreaches a stable, low value. Upon completion of aging, capacitors arere-filled to replenish lost electrolyte, and the fill-port 160 is sealedas, for example, by laser welding a closing button or cap over theencasement opening.

FIGS. 8 and 9 are a side cross-sectional and scaled cross-sectionalviews of an electrolytic capacitor suitable for use in an implantablemedical device in accordance with a further embodiment of the presentinvention. In this case, cathode material is deposited on two substrates146 (e.g. titanium) which are separate from encasement 148. Beforecathode deposition, the substrates may be chemically or mechanicallymodified to increase surface area. Methods suitable for this purposeinclude, but are not limited to, etching, abrasion, and medium blasting.

As previously described, an insulative separator is heat sealed around athin, D-shaped, anode (e.g. tantalum) having an imbedded lead wire 144(e.g. tantalum) imbedded therein as is shown in FIGS. 8, 9, and 11.Anode 140 is sandwiched between two cathodes 146. Additional layers ofinsulative separator material 162 are utilized between encasement 148and cathodes 146 so as to prevent unwanted electrical contact betweenthe cathodes and the encasement sidewalls. Alternatively, the cathodesmay be sealed in separators thus eliminating the need for a separator onthe anode. Of course, encasement 148 may be utilized as a cathodeterminal by simply electrically coupling cathodes 146 to the encasementInsulative material 162 may comprise polymer sheets, formed polymercaseliners, polymer coated cases, sputtered insulating oxides, etc. Asalready described in connection with FIGS. 5, 6, and 7, the electrodestack shown in FIG. 9 is inserted into the encasement, and the embeddedanode lead wire is resistance or laser welded to a feedthrough leadwire. A cover is assembled over the electrode stack, and the assembly iscompleted by means of, for example, laser welding.

As stated previously, the outer metal encasement structure of a knownplanar capacitor generally comprises two symmetrical half shells thatoverlap and are then welded along their perimeter seam to form ahermetic seal. Such a device is shown in FIG. 10. That is, theencasement comprises a case 164 and an overlapping cover 166. Aseparator sealed anode 168 is placed within case 164, and a polymerspacer ring 170 is positioned around the periphery of anode assembly168. Likewise, a metal weld ring 172 is positioned around the peripheryof spacer ring 170 proximate the overlapping portion 174 of case 164 andcover 166. The overlapping portions of case 164 and cover 166 are thenwelded along the perimeter seam to form a hermetic seal.

This technique presents certain concerns relating to both device sizeand manufacturing complexity. The use of overlapping half-shieldsresults in a doubling of the encasement thickness around the perimeterof the capacitor thus reducing the available interior space for theanode. Thus, for a given size anode, the resulting capacitor is larger.Furthermore, space for anode material is reduced due to the presence ofweld ring 172 and insulative polymer spacer ring 170. This device ismore complex to manufacture and therefore more costly.

FIG. 11 is a cross-sectional view illustrating one of the novel aspectsof the present invention. In this embodiment, the encasement iscomprised of a shallow drawn case 176 and a cover or lid 178. Thisshallow drawn encasement design uses a top down welding approach.Material thickness is not doubled in the area of the weld seam as wasthe situation in connection with the device shown in FIG. 10 thusresulting in additional space for anode material.

Cover 178 is sized to fit into the open side of shallow drawn metal case176. This results in a gap (e.g. from 0 to approximately 0.002 inches)in the encasement between case 176 and cover 178 that could lead to thepenetration of the weld laser beam thus potentially damaging thecapacitor's internal components. To prevent this, a metalized polymericweld ring is placed or positioned around the periphery of anode 168.Weld ring 180 is somewhat thicker than the case to cover gap 182 tomaximize protection. Metalized weld ring 180 may comprise a polymerspacer 186 having a metalized surface 184 as shown. Metalized weld ring180 provides for both laser beam shielding and anode immobilization. Themetalized polymer spacer 180 need only be thick enough to provide abarrier to penetration of the laser beam and is sacrificial in nature.This non-active component substantially reduces damage to the activestructures on the capacitor.

Metalized polymer spacer 180 is placed around the perimeter of anode 168during assembly and may be produced my means of injection molding,thermal forming, tube extrusion, die cutting of extruded or cast films,etc. Spacer 180 may be provided through the use of a pre-metalizedpolymer film. Alternatively, the metal may be deposited during aseparate process after insulator production. Suitable metallizationmaterials include aluminum, titanium, etc. and mixtures and alloys.

FIG. 12 is a cross-sectional view illustrating an alternative to theembodiment shown in FIG. 11. Again, the encasement comprises a case 176and a cover or lid 178 resulting in gap 182. The anode assembly 168 ispositioned within the encasement as was the situation in FIG. 11. Toprotect the capacitor's internal components from damage due to the weldlaser beam, a metalized tape 184 is positioned around the perimeter ofanode 168.

The embodiments shown in FIGS. 11 and 12 not only have space savingaspects in the encasement design, but the components are simple andinexpensive to produce. The top down assembly facilitates fabricationand welding processes. The thinness of the weld ring/spacer 180 ormetalized tape 184 reduces the need for additional space around theperimeter of the capacitor thus improving energy density. The designlends itself to mass production methods and reduces costs, componentcount, and manufacturing complexity.

As stated previously, a major disadvantage of prior art electrolyticcapacitors resides in the complexity of producing a proper weld jointbetween the anode terminal and the feedthrough terminal. That is, theanode lead wire (e.g. tantalum) is imnbedded into the anode and isjoined, by means of, for example, laser welding, to the feedthrough leadwire. This is typically accomplished by forming a “J” shape with each ofthe lead wires, pressing them together, and laser welding the interface.This is either performed prior to welding the feedthrough ferrule intothe encasement, or alternatively, sufficient space must be provided tofacilitate clamping and welding when the anode assembly is in theencasement. The former approach results in significant manufacturingcomplexity while the latter negatively impacts the size of thecapacitor.

FIG. 13 illustrates a first technique for coupling an anode lead wire toa feedthrough lead wire which substantially avoids the above notedproblems. Referring to FIG. 13 a weld block (e.g. tantalum) 190 ispositioned at the internal end of feedthrough 154 such that feedthroughlead wire 152 is in electrical engagement therewith. In this case,feedthrough 154 is made of an insulative material (e.g. a glass orpolymer) in order to electrically isolate anode lead wire 144 fromencasement 148. When anode 140 having anode lead wire 144 imbeddedtherein is positioned within encasement 148, anode lead wire 144 rests,in part, on weld block 190. Electrical coupling between anode lead wire144 and weld block 190 may be accomplished by techniques such as laserwelding, parallel gap welding, etc. The need for bends in the lead wireshas been eliminated thus reducing fixturing and manufacturingcomplexity. In fact, weld block 190 may contain locating or holdingfeatures (e.g. grooves) that entirely eliminate the requirement forfixturing. Weld block 190 may be provided with appropriate insulation toprevent shorting to encasement 148. The size of the capacitor is reducedbecause it is no longer necessary to provide internal bends and weldjoints in the lead wires. The reliability of the resulting structure isimproved because the use of a polymeric feedthrough permits theutilization of materials that are more stable, and the elimination ofinternal weld joints reduces manufacturing costs and complexity.

FIG. 14 illustrates another arrangement for electrically coupling theanode to an external lead wire. As was the case previously, afeedthrough ferrule 154 is positioned within encasement 148 and isconfigured such that feedthrough lead wire 152 is accessible from theexterior of capacitor encasement 148. A weld block 190 is positioned atthe internal end of feedthrough ferrule 154 in electrical engagementwith lead wire 152. In this case however, anode 140 is likewise providedwith weld block 192, and electrical coupling between weld block 192 andweld block 190 is accomplished by means of, for example, a conductiveribbon 194 electrically coupled, as for example by welding, to bothanode weld block 192 and feedthrough weld block 190.

FIG. 15 illustrates yet another arrangement for electrically couplinganode lead wire 144 to feedthrough lead wire 152. An intermediate weldblock (e.g. tantalum) 196 is provided within capacitor encasement 148and is configured such that an internal end of a lead wire 152 and anend of anode lead wire 144 contact weld block 196 when anode 140 ispositioned within encasement 148. Anode lead wire 144 and feedthroughlead wire 152 are then electrically coupled to weld block 196 using anyknown technique such as laser welding.

Yet another arrangement for coupling anode lead wire 144 to feedthroughlead wire 152 utilizes a small sleeve or piece of tubing 198 made of anelectrically conductive material (e.g. tantalum). Referring to FIG. 16,anode lead wire 144 and feedthrough lead wire 152 are received withinsleeve 198 and may be electrically coupled thereto by means of, forexample, welding or crimping. An opening 200 may be provided in sleeve198 so as to permit additional welding along the length of the leads.Sleeve 198 provides the necessary fixturing for lead wires 144 and 152,and due to it's small size, the use of sleeve 198 is conducive to devicedownsizing. Sleeve 198 may be imbedded in anode 140 eliminating the needfor anode lead wire 144 as is shown in FIG. 17. Alternatively, sleeve198 may be integrally coupled or formed with feedthrough ferrule 154 asis shown in FIG. 18.

Thus, there has been provided an electrolytic capacitor that is not onlyeasier and less costly to manufacture, but one which may be made smallerfor a given capacitance. The inventive capacitor is therefore suitablefor use in implantable medical devices such as defibrillators, even assuch devices become smaller and smaller.

What is claimed is:
 1. A capacitor structure, comprising: a shallowdrawn case having a first major side and a peripheral wall extendingtherefrom, said first major side having a first interior surface andsaid wall having a peripheral interior surface; a lid sealingly coupledto said case along adjacent edges of said lid and said wall, said lidand said case forming an encasement of said capacitor structure, saidlid comprising a second interior surface; a cathode material disposedproximate said first and second interior surfaces; an anode positionedintermediate the cathode material and having peripheral portionpositioned proximate said adjacent edges; a protective layer on saidperipheral portion to protect said anode when said lid is sealinglycoupled to said case; and a first insulative separator between saidanode and said cathode material.
 2. A capacitor structure according toclaim 1 further comprising an electrolyte within said encasement and incontact with said cathode material and said anode.
 3. A capacitorstructure according to claim 1 wherein said protective layer comprises ametalized ring.
 4. A capacitor structure according to claim 3 whereinsaid metalized ring comprises a polymer spacer having a metalizedsurface.
 5. A capacitor structure according to claim 1 wherein saidprotective layer comprises a metallized tape.
 6. A capacitor structureaccording to claim 1 further comprising a second insulative separatorpositioned between said cathode material and said first and secondinterior surfaces.
 7. A capacitor structure according to claim 6 whereinsaid cathode material is electrically coupled to said encasement, saidencasement forming a cathode terminal.
 8. A capacitor structureaccording to claim 1 wherein said cathode material comprises carbon ontitanium carbide.
 9. A capacitor structure according to claim 1 whereinsaid cathode material comprises carbon and silver vanadium oxide ontitanium carbide.
 10. A capacitor structure according to claim 1 whereinsaid cathode material comprises carbon and crystalline manganese dioxideon titanium carbide.
 11. A capacitor structure according to claim 1wherein said cathode material comprises platinum on titanium.
 12. Acapacitor structure according to claim 1 wherein said cathode materialcomprises ruthenium on titanium.
 13. A capacitor structure according toclaim 1 wherein said cathode material comprises silver vanadium oxide ontitanium.
 14. A capacitor structure according to claim 1 wherein saidcathode material comprises barium titanate on titanium.
 15. A capacitorstructure according to claim 1 wherein said cathode material comprisescarbon and crystalline ruthenium oxide on titanium carbide.
 16. Acapacitor structure according to claim 1 wherein said cathode materialcomprises carbon and crystalline iridium oxide on titanium carbide. 17.A capacitor structure according to claim 1 wherein said capacitorstructure includes a feedthrough in said encasement through whichelectrical coupling may be made between said anode and an externalterminal.
 18. A capacitor structure according to claim 17 wherein saidfeedthrough is made of a polymeric material.
 19. A capacitor structureaccording to claim 18 wherein said feedthrough forms a hermetic sealwith said encasement.
 20. A capacitor structure according to claim 17further comprising: an anode lead coupled to said anode; and a terminallead extending through said feedthrough.
 21. A capacitor structureaccording to claim 20 further comprising a conductive sleeve forreceiving said anode lead at a first end thereof and said terminal leadat a second end thereof.
 22. A capacitor structure according to claim 21wherein said anode lead and said terminal lead are electrically coupledto said sleeve by welding.
 23. A capacitor structure according to claim21 wherein said anode lead and said terminal lead are electricallycoupled to said sleeve by crimping.
 24. A capacitor structure accordingto claim 21 wherein said sleeve includes an aperture thereinintermediate said first end and said second end.
 25. A capacitorstructure according to claim 20 further comprising a weld block forcoupling said anode lead to said terminal lead.
 26. A capacitorstructure according to claim 20 further comprising a first weld blockcoupled to said feedthrough.
 27. A capacitor structure according toclaim 26 further comprising a second weld block coupled to said anode.28. A capacitor structure according to claim 27 further comprising anelectrical coupling between said first and second weld blocks.
 29. Acapacitor structure according to claim 17 further comprising aconductive sleeve for electrically coupling said anode through saidfeedthrough.
 30. A capacitor structure according to claim 29 whereinsaid conductive sleeve is imbedded in said anode.
 31. A capacitorstructure according to claim 29 wherein said conductive sleeve isattached to said feedthrough.
 32. A capacitor structure for use in animplantable medical device, said capacitor comprising: a shallow drawncase having a first major side and a peripheral wall extendingtherefrom, said first major side having a first interior surface andsaid wall having a peripheral interior surface; a lid scaling coupled tosaid case along adjacent edges of said lid and said wall, said lid andsaid case forming an encasement of said capacitor structure, said lidcomprising a second interior surface; a cathode material disposedproximate said first and second interior surfaces; an anode positionedintermediate the cathode material and having peripheral portionpositioned proximate said adjacent edges; a protective layer on saidperipheral portion to protect said anode when said lid is sealingcoupled to said case; a first insulative separator between said anodeand said capacitive material; an electrolyte within said encasement andin contact with said cathode material and said anode; and a feedthroughin said encasement through which electrical coupling may be made betweensaid anode and an external terminal.
 33. A capacitor structure accordingto claim 32 wherein said protective layer comprises a metalized ring.34. A capacitor structure according to claim 32 wherein said metalizedring comprises a polymer spacer having a metalized surface.
 35. Acapacitor structure according to claim 32 wherein said protective layercomprises a metallized tape.
 36. A capacitor structure according toclaim 32 further comprising a second insulative separator positionedbetween said cathode material and said first and second interiorsurfaces.
 37. A capacitor structure according to claim 36 wherein saidcathode material is electrically coupled to said encasement, saidencasement forming a cathode terminal.